The invention relates to a retention and triggering mechanism with a shape memory actuator.
In space technology it is known (DE-A1-196 49 739) to hold a wire which is subjected to tensile stress by its curved ends by means of a fusible wire which melts when a current is applied to it, thus releasing the wire. The wire which is subjected to tensile stress, shaped as a coil, keeps together two halves of a divided bolt mounting. When the wire is released, the two halves of the bolt mounting hinge apart under spring pressure, and the bolt can detach itself from the bolt mounting. The bolt is for example used to keep solar cell panels of a space vehicle pressed together during the start of the rocket, said solar cell panels being released by detaching the bolts when the location of the mission has been reached. The use of a fusible wire is associated with the disadvantage of unreliable and undefined triggering.
U.S. Pat. No. 5,129,753 discloses a retention and triggering mechanism with a shape memory actuator. A shape memory wire is used which at the time of triggering becomes shorter as a result of an increase in its temperature, thus lifting a securing sleeve from its rest position. During this action, the securing sleeve releases a chuck comprising several latch elements which fold out and release a gudgeon, thus releasing the connection.
U.S. Pat. No. 5,160,233 discloses a bolt mounting with a shape memory actuator for use in space technology; it is used for jettisoning empty fuel tanks which are held on the outside of a space vehicle by means of a bolt. The known bolt-mounting releases the bolt by temperature-control, by pushing apart cylinder segments in the bolt mounting which, with their interior thread, encompass from the outside the thread of the bolt. Pushing apart is effected in such a way that a cylindrical shape memory actuator lifts the cylinder segments together with the bolt into a position which in the bolt mounting permits lateral moving apart of the cylinder segments, and in that moving apart of the cylinder segments takes place by the actuator, which at its front is of truncated cone shape, entering an annular aperture formed by the cylinder segments. When the temperature is increased, the shape memory actuator extends in longitudinal direction, thus causing the above-described lifting and pushing apart of the cylinder segments. Temperature increase to cause triggering takes place via the Joule effect. Pushing apart the cylinder segments requires a relatively large and powerful actuator and when the parts slide one on top of the other in the bolt mounting, problems with regard to cold welding may occur. The cylinder segments, their fixation in the retention state, and the means for moving them apart in the triggering state, require a design which is relatively expensive from the point of view of construction.
It is thus the object of the invention to create a retention and triggering mechanism with a shape memory actuator, which ensures safe triggering, a simple design and low energy requirements.
According to the invention, this object is met by the characteristics of claim 1. Further embodiments of the invention are stated in the subordinate claims.
The retention and triggering mechanism according to the invention has the advantage that it comprises only a few parts, that due to its compact design it can easily be integrated in existing designs and thus simplifies known structures. The retention mechanism according to the invention provides a further advantage in that there are no components which need to be blasted away, as is the case e.g. with a pyrotechnical release, and that no parts are destroyed during release. When shape memory alloys are used which have been pre-treated in a special mechanical process step, the austenite start temperature is significantly above the values of commercially available TiNi alloys. If such alloys are used, the wire retainers according to the invention can be used to advantage even at higher ambient temperatures, such as may occur e.g. during space travel missions.